Green’s Dictionary of Slang

gallagher and shean n.

[pun on Gallagher and Shean, Irish/Jewish vaudeville stars, touring America from 1920–25; Gallagher was Ed Gallagher (c.1872–1929); Shean was the Marx Brothers’ uncle, Al Schoenberg (1868–1949), who wrote their hit show Home Again in 1914]

(US) a two-man police team.

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[US]Goldin et al. DAUL 77/1: Gallagher and Shean. (Obs.) The policeman-sergeant team formerly seen patrolling the streets of big metropolises in police cars.